1. Field of the Invention (Technical Field)
The present invention relates to a portable drill apparatus and system which utilizes the electrohydraulic technique (the creation of shock wave and pressure wave from an underwater spark or plasma) which provides high drilling rates and is useful for the purpose of drilling shallow holes (a few meters in depth) in underground mines and above ground mining and construction applications. The drill utilizes electrical power from an attached pulse generator to create intense shock waves in the electrode area to crush rock or other material. Water flush is provided through the cable and the drill stem to sweep out the cuttings. The drill support and advance mechanism is utilized to advance the drill through the rock.
2. Background Art
One of the ongoing needs for small drills in the mining industry is the drilling of roofbolt holes for supporting the mine roof and the drilling of explosive holes for inserting explosives, removing the ore from the mine face. Conventional drill technology utilizes a star bit and an air hammer to provide drilling action in drilling the holes. These machines are very noisy, the drill tip needs frequent replacement and the overall efficiency of this system is very poor (near 1%). Perhaps, most significantly, the drill cannot be utilized in areas where the distance from the floor to the ceiling is short (of the order of 1-1.5 meters), because of the need to utilize solid rod for the drilling process. The same is true of drills utilizing a rotary motion for the drilling process. In all of these cases, it is not possible for the drill to drill into the roof for a hole depth that is longer than the drill itself. For example, it is not possible for one of these drills operating in a 1.5 meter floor-to-ceiling height to drill a hole in the roof 3 meters deep. In addition, these drills require significant pressure exercised against the rock by the operator in order to provide the cutting action. This places the operator at risk because of the potential fall of rock from the roof onto the operator during the drilling process.
The electrohydraulic process has been used for some period of time for creating shock waves in water (see U.S. Pat. No. 4,471,405, entitled "Focused Shock Spark Discharge Drill Using Multiple Electrodes," to Moeny, et al.). The '405 Patent teaches the use of a pulse forming line to control power flow into the head of a drill utilizing the electrohydraulic process. The pulse forming line is connected to an array of electrodes which forms a spark array. One of the electrodes of each of the array is connected to the high voltage side of the pulse forming line and the other electrodes are at ground potential. When discharged in a liquid, these electrodes produce intense focused shock waves that can pulverize or fracture rock. By delaying the firing of each group of electrodes, the drill can be steered within the earth. Power can be fed to the pulse forming line either downhole or from the surface.
The significant technology issues that must be solved in order to utilize electrohydraulic (EH) rock crushing for drilling in a mining situation include power control to the electrodes, flashover suppression inside the drill, shock wave control, and electrode erosion. Secondly, the electrical pulse that is delivered to the drill must be controlled so that the plasma that is created in the water has the proper relationship of current with time to create the shock wave or pressure wave for efficient and effective crushing of the rock. However, the hardware must then accommodate this pulse so as to provide the high voltage necessary to achieve breakdown at the drill tip without causing breakdown elsewhere in the portable drill stem, especially in the region near but not at the electrodes.
In order to overcome the problems of the prior art, it is necessary to prevent the rock crushing process itself from also crushing the insulator and thus destroying the operation of the drill. Directing the shock wave to the surface to be crushed, and preventing it from crushing key internal portions of the drill is also required for a successful portable electrohydraulic drill. Further, a system to prevent the rock dust from contaminating the insulator thus leading to high voltage flashover across the insulator and destruction of the insulator is needed. All electrohydraulic plasmas erode the electrodes. The physical process is caused by the interaction of the plasma with the molten electrode material. It is unavoidable for practical purposes. Therefore, means to deal with electrode erosion is also required if the electrohydraulic process is to be used for drilling.